Dyeing of polyacrylonitrile with vat dyes



DYEING OF POLYACRYLONITRILE WITH VAT DYES Jerry M. Mecco, Somerville, and Joseph W. Cre'ely, East Bound Brook, N. J., assignors to American Cyanamid Company, New York-,N'. Y., a corporation of Maine No Drawing. Application May 17, 1952,

Serial No. 288,541 I 5 Claims. (Cl. 834) This invention relates to a; process of dyeing certain types of polyacrylonitrile synthetic fibers with vat dyes.

Polyacrylonitrile fibers both infilament and staple form have achieved extensive commercial success. In general, there are two types of spinning processes. In the one, the polymer is dissolved in. an organic solvent such as diethyl formamide and forced through the spinnerette opening into an atmosphere which results in rapid evaporation of the solvent. This spinning process is used, for example, by the DuPont Company in producing their fiber under their trade-mark Orlon. Anotherprocess of spinning is a Wet process in which the polymer is dissolved i d States Patent '0 in a strong aqueous thiocyanate. solution and extruded into a suitable bath. The wet spinningprocess is applicable both to pure polymerized acrylonitrile'and to copolymers of acryloni-trile with small amounts of other substances such as acrylates, vinyl pyridine andthe like- Although polyacrylonitrile whether spun by the organic solvent or dry method or the aqueous thiocyanate method, is probably chemically the' same substance, the surfaces appear to be ditferent which difierence may be physical or chemical or both.

It has been attempted in the past to dye polyacrylonitrile fibers produced by either wet or dry spinning with: vat dyes, in order to obtain the important advantages of vat dyes such as high light fastness and fastness to many other treatments. In the past,-however, the ordinary vvat dyeing procedure has not been applicable at all to fibers spun from solutions in organic solvents and has not been entirely satisfactory, at least fordeep shades even' with pH range of from 6 to 8 and preferably between about 6.5;

and 7.5. In this range the reduced or leuco' form of the vat dyestuff exists in the form of the compound with free hydroxyl groups and notin the form of the sodium salt as is in ordinary vat dyeing procedures at higher pHs. The free hydroxy leuco form has-been sometimes referred to rather loosely as a vatacid, although it is only an acid in the sense that it is capable of forming compounds with strong bases which is true of most phenols.

The pH range of the present invention is extremely critical, particularly at its upper limit. The moment that the pH is high enough to form the sodium salt of the vat acid, the advantages of the present invention cease and effective dyeing, particularly of a dark shade is impossible. On the other hand, within the pH range of the present invention, excellent dyeing permitting the production of dark shades is possible. It is not known why the nature of the spinning process should be so decisive in theefiectiveness of the present process. Obviously, the surface of the fiber has been affected by the spinning process used,

and it is not desired to limit the present invention to any types.

'ice

' 2 theory of action or of chemical or physical constitution of the surfaces of the spun fibers.

While the pH range is the most critical and the most important feature of the present invention, it has been found that temperature is also an important factor, and in general, quite high temperature should be used with some dyes and particularly in the case of some of the a'crylonitrile copolymer fibers it is possible to dye at temperatures below the boiling point of water down to as low as F. Improved results are, however, normally obtained by dyeing at the. boil and with many dyes still better results are obtained at higher temperatures up to or around 300 F. or even slightly higher. In general, the top temperature' limit is not one which is determined by dyeing efficiency but is dictated by the temperature at which damage to the fiber results. In general, it may be considered that 325 F. will represent a top' limit at which some damage may be noticeable but can betolerated' if the dyeing is effected very readily.

The critical limitation as to pH range can be met by any method desired, thus it is even possible to maintain the pH range with dilute solutions of a strong alkali such as sodium hydroxide. However, such methods of maintaining the pH range while effective require very careful control because within the pH range close to neutral a very small amount of alkali will make a great pH change. The reduction of the dye itself tends to lower the pH because the sodium hydrosulfite used is oxidized to sodium bisulfate which is distinctly acid and therefore results in a lowering of the pH. The necessity of careful control makes it desirable to use a buifer'rather than to maintain the pH by very careful addition of alkali, and accordingly, in its preferred-'- em'bodi'me'nt the present invention includes the use ofsuit'able buffers. The two best buffers which have been found are sodium tripolyphosphate and sodium tetraphosphate, the former giving the most reliable and complete buffering action. It should be understood that the bulfers do not appear to act chemically other than the control of pH because the dyeing procedure appears to depend on the pH regardless of how it is maintained.

' It is an important advantage of the present invention that more dye and reducing agent can be added at any time during the dyeing process which is often difiicult or not feasible" at all with the ordinary vat dyeing procedure. A very delicate and continuous control is thus made possible.

Polyacrylonitrile fibers are subject to yellowing or dulling which will often result in producing a relatively dull dyed material. These two undesirable changes are of two One, which results when the fiber is exposed to alkali which is irreversible result and can be removed by acidification. It is no problem in the present invention which is not carriedoutat a high pH. 7 The second form of yellowing appears to be a temperature and time phenomenon and is not reversible. Although the dyeing is extremely rapid at high temperatures in the process of the present invention, still there may be some yellowing due-to heat. It has been found that fibers whichare copolymers, particularly acrylate copol-ymers, may be protected from heat yellowing or the yellowing greatly reduced by the addition to the dye bath of compounds of polyvalent metals in the state of oxidation in which they exert no oxidizing elfect. The most important element is zirconium, the compounds of which exert a maximum anti-yellowing elfect. Other eifective elements are manganese and magnesium while somewhat less effective compounds are those of calcium and aluminum.

In a more specific aspect of the present invention when used for dyeing acrylonitrile copolymer fibers the addition ofv anti-yellowing compounds. is also. included. It is not known why the metal compounds referred to above exert such a marked effect on heat yellowing with the acrylonitrile copolymer fibers and yet do not appear to have any practically useful effect with pure polyacrylonitrile. It is not desired therefore to limit the invention to any theory of how these metal compounds act.

The polyvalent metal compounds referred to above should not be confused with the use of cuprous compounds in the so-called cuprous ion method of dyeing. This is a method in which a cuprous ion is formed in the dye bath and has been extensively employed in introducing various dyestuffs in a nonbasic polymerized synthetic fibers which would not otherwise have affinity for the fiber. Therefore, the term polyvalent as used in the present invention should be interpreted in its normal restricted meaning, namely, that the metal will unite with more than one equivalent of a monobasic anion. Cuprous compounds show copper with a net valence of 1, that is to say, when a compound with a monobasic anion such as chlorine is formed there are as many atoms of chlorine as of copper. Although in the actual structural formula of the compounds, copper is usually assumed to have a valence of 2, 1 valence being connected to the other copper atom. In the present invention, however, only the net valence toward anion is considered and the term polyvalent is used in this sense only. It does not include cuprous compounds which are just as ineffective in the present invention as any other monovalent metals.

The invention will be described in greater detail in conjunction with the following specific examples, the parts being by weight except where otherwise specified.

Example 1 A dye bath was prepared containing 0.15 part of a green vat dyestufi Color Index 1101, 1 part of sodium tripolyphosphate, 0.75 part of sodium hydrosulfite and 200 parts of water. This bath was heated to 160 F. and then 5 parts of a solution of manganous chloride with 6 moles of water of crystallization added. In the bath was dyed 5 parts of thiocyanate spun filament yarn of acrylonitrile copolymerized with a small amount of methyl acrylate. The dyeing was continued at 160 C. until complete and the bath then slowly cooled. Thereupon the material was removed, boiled in 400 parts of an aqueous solution containing 5 parts of sodium carbonate and 0.5 part of soap. The yarn was then rinsed and dried.

The resultant dyeing was an excellent green shade being much stronger and brighter than a corresponding dyeing prepared under identical conditions but without the manganous chloride in the bath.

Example 2 A dye bath was prepared containing parts of a 1% aqueous slurry of paste of a vat dye of Example 1, 1 part of sodium tripolyphosphate, 0.75 part of sodium hydrosulfite and 200 parts of water. The bath was heated to the boil and 5 parts of a 10% solution of zirconium oxychloride added.

In the bath there was dyed 5 parts of acrylonitrile copolymer filament yarn as described in Example 1. After the dyeing was complete, the material was removed from the bath and boiled with a 1% aqueous solution of sodium carbonate. Thereupon the material was boiled in a 0.1% soap solution, rinsed and dried.

The resultant dyeing was much greener than a corresponding dyeing prepared under identical conditions except that the zirconium oxychloride was not present in the dye bath.

Example 3 A dye bath was prepared with 15 parts of a 1% slurry of a green vat dyestuff, Color Index 1101, described in Example 2, 1.3 parts of sodium tripolyphosphate and 200 parts of water. This bath was heated to the boil and 0.1 part sodium hydrosulfite and 3.3 parts of a 10% aqueous The procedure of Example 3 was followed but the boiling was continued for three times as long as in Example 3. The results were identical. This shows that the relatively better results obtained with the manganous chloride were not due to an insufficient dyeing time of the dyeing which did not have the manganous chloride present.

Example 5 The procedure of Example 3 was followed. The boiling time was 12 times as long. No substantial difference in dyeing result was noted over Examples 3 and 4.

Example 6 The procedure of Example 3 was repeated with 4 different amounts of manganous chloride, namely, 5 parts, 2.5 parts, 0.5 part and a control with no manganous chloride present. Oxidation was effected by dipping in a 1% sodium carbonate solution, followed by treatment with a hot 1% solution of sodium perborate. The appearance of the dyeing showed a regular improvement from a rather poor violet color when no manganous chloride was present to a green of maximum strength when 5 parts of the solution were present.

Example 7 The procedure of Example 6 was followed replacing the manganous chloride with 3.3 parts of a 10% solu tion of calcium chloride. Results were obtained which were very similar to those of Example 6.

Example 8 The procedure of Example 7 was followed using Vat Yellow GC (1,2,5,6-anthraquinone-C-diphenyl dithiazole). Excellent results were obtained much stronger than the corresponding dyeing under identical conditions in the bath in which the calcium chloride was omitted.

Example 9 The procedure of Example 8 was followed replacing the Vat Yellow GC with Vat Olive T (6-benz-1-dianthraquinonylamino BzN2,2-acridine). Again two dyeings were made, one without calcium and one with calcium. The dyeing with calcium in the bath showed markedly improved strength.

Example 10 The procedure of Example 7 was repeated using Vat Red BN Color Index 1162. Here again the dyeing in the bath containing the calcium chloride was markedly better than the corresponding dyeing in which the calcium v chloride was omitted.

Example 11 The procedure of Example 1 was followed omitting the manganous chloride and the sodium tripolyphosphate and substituting for the latter one part by volume of a 30 B. of aqueous sodium hydroxide. The results obtained were the same as with the sodium tripolyphosphate.

Example 12 Four parts of a commercial paste of Vat Violet 68 Color Index 1212 was mixed with 30 parts by volume of a 10% solution of sodium tripolyphosphate and 2 parts of sodium hydrosulfite. The mixture was brought to a boil and water added to make up a total volume of 200 parts, the mixture being cooled to room temperature. Five parts of a skein of filament of pure polyacrylonitrile spun from concentrated aqueous thiocyanate solution was introduced as a skein. The bath was raised slowly to the boil, the boil continued until dyeing was complete. The yarn was taken from the bath, washed in warm water and then boiled for five minutes in a soda ash solution. This was followed by washing with warm water and finishing with a wash of a solution of 2.5 parts of sodium dodecyl sulfate per gallon. This last wash was efiected at the boiling temperature. The

yarn dyed a strong violet showing good fastness.

Example 13 The procedure of Example 12 was followed using staple fiber instead of filament. Excellent penetration and a level shade was obtained.

Example 14 An acrylonitrile copolymerized staple spun as described in Example 1 was dyed with dimethoxydibenzanthrone, Jade Green, in a bath containing 3% sodium tripolyphosphate and 2% sodium hydrosulfite. The temperature was 250 F. and after dyeing the dye was oxidized on the fiber by boiling with 1 part by volume of hydrogen peroxide containing 1% acetic acid. A wellpenetrated, level medium green dyeing resulted.

We claim:

1. A method of dyeing with vat dyes polyacrylonitrile fibers which are copolymers of acrylonitrile and a small amount of methyl acrylate and spun from a concentrated aqueous thiocyanate solution, which comprises heating at a temperature between 160325 F. the said fibers in an aqueous dyebath containing an unesterified leuco vat dyestufi, a reducing agent and a suificient amount of zirconium oxychloride to substantially reduce heat yellowing of said fiber, the dyebath having a pH between 6 and 8, maintaining the pH of said aqueous dyebath between 6 and 8 during said heating until the dyeing is complete and oxidizing the dyestufi on the fiber.

2. As a method of dyeing polyacrylonitrile fibers containing copolymers of a major amount of acrylonitrile and a minor amount of methyl acrylate copolymerized together and spun from a concentrated aqueous thiocyanate solution of said copolymers, with vat dyes, the improved method which comprises heating said fibers in an aqueous dyebath having a pH between 6 and 8 and containing an unesterified leuco vat dye, a reducing agent, a sodium polyphosphate bufier and a soluble, non-oxidizing, polyvalent metal chloride which is capable of reducing the heat yellowing of said fibers, at a temperature between 212 and 300 F., maintaining the pH of said aqueous dyebath between 6 and 8 during said heating thereof by means of said buffer until the dyeing is complete and oxidizing the dyestuff on the fiber.

3. The process of claim 2 wherein the said polyvalent salt is zirconium oxychloride.

4. The process of claim 2 wherein the said polyvalent salt is manganous chloride.

5. The process of claim 2 wherein the said polyvalent salt is calcium chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,012,073 Schirm Aug. 20, 1935 2,067,928 Kern Jan. 19, 1937 2,548,544 Mecco Apr. 10, 1951 2,548,545 Mecco Apr. 10, 1951 2,646,339 Ward July 21, 1953 OTHER REFERENCES Chem. Tech of Dyeing and Printing, by L. Diserens, published New York city, 1948, by Reinhold Publishing Corp, pp. and 136. (Available in Patent Ofi'ice Library.)

American Dyestuif Reporter, January 22, 1951, pp. P51, P52.

American Dyestutf Reporter, September 17, 1951, pp. P588 to P590. 

1. A METHOD OF DYEING WITH VAT DYES POLYACRYLONITRILE FIBERS WHICH ARE COPOLYMERS OF ACRYLONITRILE AND A SMALL AMOUNT OF METHYL ACRYLATE AND SPUN FROM A CONCENTRATED AQUEOUS THIOCYANATE SOLUTION, WHICH COMPRISES HEATING AT A TEMPERATURE BETWEEN 160*-325* F. THE SAID FIBERS IN AN AQUEOUS DYEBATH CONTAINING AN UNESTERIFIED LEUCO VAT DYESTUFF, A REDUCING AGENT AND A SUFFICIENT AMOUNT OF ZIRCONIUM OXYCHLORIDE TO SUBSTANTIALLY REDUCE HEAT YELLOWING OF SAID FIBER, THE DYEBATH HAVING A PH BETWEEN 6 AND 8, MAINTAINING THE PH OF SAID AQUEOUS DYEBATH BETWEEN 6 AND 8 DURING SAID HEATING UNTIL THE DYEING IS COMPLETE AND OXIDIZING THE DYESTUFF ON THE FIBER. 